Identity and functional characterisation of the transporter supporting the Na+ -dependent high-affinity NO3 - uptake in Zostera marina L.
- Publisher:
- Wiley
- Publication Type:
- Journal Article
- Citation:
- Plant Cell Environ, 2023, 46, (9), pp. 2851-2866
- Issue Date:
- 2023-09
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Zostera marina is a seagrass, a group of angiosperms that evolved from land to live submerged in seawater, an environment of high salinity, alkaline pH and usually very low NO3 - . In 2000, we reported the first physiological evidence for the Na+ -dependent high-affinity NO3 - uptake in this plant. Now, to determine the molecular identity of this process, we searched for NO3 - transporters common to other vascular plants encoded in Z. marina's genome. We cloned two candidates, ZosmaNPF6.3 and ZosmaNRT2 with its partner protein ZosmaNAR2. ZosmaNAR2 expression levels increase up to 4.5-fold in Z. marina leaves under NO3 - -deficiency, while ZosmaNRT2 and ZosmaNPF6.3 expressions were low and unaffected by NO3 - . NO3 - transport capacity, kinetic properties and H+ or Na+ -dependence were examined by heterologous expression in the Hansenula polymorpha high-affinity NO3 - transporter gene disrupted strain (∆ynt1). ZosmaNPF6.3 functions as a H+ -dependent NO3 - transporter, without functionality at alkaline pH and apparent dual kinetics (KM = 11.1 µM at NO3 - concentrations below 50 µM). ZosmaNRT2 transports NO3 - in a H+ -independent but Na+ -dependent manner (KM = 1 mM Na+ ), with low NO3 - affinity (KM = 30 µM). When ZosmaNRT2 and ZosmaNAR2 are co-expressed, a Na+ -dependent high-affinity NO3 - transport occurs (KM = 5.7 µM NO3 - ), mimicking the in vivo value. These results are discussed in the physiological context, providing evidence that ZosmaNRT2 is a Na+ -dependent high-affinity NO3 - transporter, the first of its kind to be functionally characterised in a vascular plant, that requires ZosmaNAR2 to achieve the necessary high-affinity for nitrate uptake from seawater.
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